ImGui::InputText freezes in v1.87+ in a Win32 IME ImmAssociateContextEx() call

[BullyWiiPlaza]

Version/Branch of Dear ImGui:

Version: v1.88
Branch: https://github.com/Microsoft/vcpkg/blob/master/ports/imgui/portfile.cmake

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_win32.cpp + imgui_impl_dx11.cpp
Compiler: MSVC
Operating System: Windows 11 Pro

My Issue/Question:

I'm using ImGui::InputText() to create text fields. Since v.187 of Dear ImGui clicking into text fields freezes the entire application (no crash but "stopped responding"). The bug does not occur with v1.86 and the bug still occurs in v1.88.

Standalone, minimal, complete and verifiable example:

std::string input_text;
ImGui::Begin("Example Bug");
ImGui::InputText("My text field", &input_text);
ImGui::End();

I researched but didn't find a clear solution or workaround (besides downgrading to v1.86). I believe my issue is similar to #4972 and #5264. How exactly would you debug into ImGui::InputText() getting stuck if needed? ImGui::InputText() takes me to the imgui_stdlib.h file and not the .cpp file and input texts are probably handled somewhere else. What exactly changed between those versions which could cause this regression? Thanks in advance for taking a look into this.

[ocornut]

Based on the multiple reports and the fact we did make changes to Win32 IME code in 1.87, I am assuming we do have an issue but I would like to understand if it is tied to debugger loading symbols or something else.

How exactly would you debug into ImGui::InputText() getting stuck if needed?

If something appears stuck, you first want to break in the debugger to find where.

What exactly changed between those versions which could cause this regression?

Answer is in the changelog:

- Platform IME: moved io.ImeWindowHandle to GetMainViewport()->PlatformHandleRaw.
- Platform IME: add ImGuiPlatformImeData::WantVisible, hide IME composition window when not used. (#2589) [@actboy168]
- Platform IME: add ImGuiPlatformImeData::InputLineHeight. (#3113) [@liuliu]
- Platform IME: [windows] call ImmSetCandidateWindow() to position candidate window.

Diffing between 1.86 and 1.87, the important related changes here are that we want from:

static void ImeSetInputScreenPosFn_DefaultImpl(int x, int y)
{
    // Notify OS Input Method Editor of text input position
    ImGuiIO& io = ImGui::GetIO();
    if (HWND hwnd = (HWND)io.ImeWindowHandle)
        if (HIMC himc = ::ImmGetContext(hwnd))
        {
            COMPOSITIONFORM cf;
            cf.ptCurrentPos.x = x;
            cf.ptCurrentPos.y = y;
            cf.dwStyle = CFS_FORCE_POSITION;
            ::ImmSetCompositionWindow(himc, &cf);
            ::ImmReleaseContext(hwnd, himc);
        }
}

to

static void SetPlatformImeDataFn_DefaultImpl(ImGuiViewport* viewport, ImGuiPlatformImeData* data)
{
    // Notify OS Input Method Editor of text input position
    HWND hwnd = (HWND)viewport->PlatformHandleRaw;
#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
    if (hwnd == 0)
        hwnd = (HWND)ImGui::GetIO().ImeWindowHandle;
#endif
    if (hwnd == 0)
        return;

    ::ImmAssociateContextEx(hwnd, NULL, data->WantVisible ? IACE_DEFAULT : 0);

    if (HIMC himc = ::ImmGetContext(hwnd))
    {
        COMPOSITIONFORM composition_form = {};
        composition_form.ptCurrentPos.x = (LONG)data->InputPos.x;
        composition_form.ptCurrentPos.y = (LONG)data->InputPos.y;
        composition_form.dwStyle = CFS_FORCE_POSITION;
        ::ImmSetCompositionWindow(himc, &composition_form);
        CANDIDATEFORM candidate_form = {};
        candidate_form.dwStyle = CFS_CANDIDATEPOS;
        candidate_form.ptCurrentPos.x = (LONG)data->InputPos.x;
        candidate_form.ptCurrentPos.y = (LONG)data->InputPos.y;
        ::ImmSetCandidateWindow(himc, &candidate_form);
        ::ImmReleaseContext(hwnd, himc);
    }
}

If you want to help I would need you to very precisely answer the following questions, one by one:

1. Are you running with a debugger attached? Does it makes any difference if you have a debugger attached or not?
2. If the "freeze" only happens with a debugger attached: have if you tried waiting for several minutes? Does Visual Studio shows a "loading symbol" window, if so, can you press ESC and does it resume the application?
3. Try commenting the line ::ImmAssociateContextEx(hwnd, NULL, data->WantVisible ? IACE_DEFAULT : 0);. Does it makes a difference?
4. Try commenting only the line ::ImmSetCandidateWindow(himc, &candidate_form);. Does it makes a difference?
5. Try commenting both lines above. Does it makes a difference?

Thank you very much!

[BullyWiiPlaza]

1. Yes, I'm running with a debugger attached. However, it does not matter if I'm using a debugger or not, the bug always occurs. Users running the release build also report this issue and they obviously don't have a debugger attached.
2. Not applicable, there is no symbols loading going on when it freezes. Generally symbols loading would take a few seconds and in this case, the process never unfreezes itself, even after minutes of waiting.
3. Yes, this fixes the bug and it no longer freezes.
4. This does not make a difference.
5. I did not try since 3. worked fine.

Thanks for the feedback.

[PathogenDavid]

@BullyWiiPlaza Do you have any third-party IMEs installed? (Or any IMEs in general?)

[BullyWiiPlaza]

@BullyWiiPlaza Do you have any third-party IMEs installed? (Or any IMEs in general?)

No, I didn't even know what IME was exactly. Also other users had the same problem and they are often using a fairly plain Windows installation. Not sure which third-party IMEs even exist out there someone might want to install. I actually have Chinese language support installed, does that matter? I don't want to go through the process of re-testing again though unless it's needed.

[ocornut]

I don't know if that's the desirable logic and haven't tested it yet, but does moving the ::ImmAssociateContextEx(hwnd, NULL, data->WantVisible ? IACE_DEFAULT : 0); call to inside the if {} block fixes it for you?

[BullyWiiPlaza]

I don't know if that's the desirable logic and haven't tested it yet, but does moving the ::ImmAssociateContextEx(hwnd, NULL, data->WantVisible ? IACE_DEFAULT : 0); call to inside the if {} block fixes it for you?

Yes, putting this line of code into the if {} block is fine as well and the freeze does not occur.

[ocornut]

Thank you for testing this. I verified that this still gets us the behavior desired by #2589.
Pushed the fix now 133bbaf

[ocornut]

My bad this actually never re-enable the IME aftet the first time.